The latest update to MW3 messed up everyone's downloads causing us to have to re-download every map pack on the first start up after the title update. For the maps you already have it will only take a second or two to re-download.
Just use the in game STORE to re-download them. It may tell you to exit to dash a few times before it completes (I had to). Once you do that you should be good to go.
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